Prediction of Lubricant's Fatigue Life in the FZG Micropitting Test

Pitting and micropitting are two key fatigue modes of failure for gears and bearings. Many pitting and micropitting rig tests have been developed in the industry to evaluate the fatigue pitting or micropitting life of lubricants. FZG pitting and micropitting tests are widely used for this purpose. We have studied pitting mechanism and developed a model to predict pitting life in the FZG pitting test carried out at 120°C. Boundary friction coefficient, EHD film thickness, and corrosivity of the lubricant and surface roughness of the gear have been found to be the four important factors affecting the lubricant's pitting life. Since today's gears are mostly made from steels containing low to non-existent inclusions, pitting is mostly initiated by micropitting. Even though this implies that rougher surface is detrimental to pitting life, we have found that this is not always the case. Since micropitting is an important fatigue failure mode, we have devoted a considerable effort on the investigation of micropitting and development of a model to predict the fatigue life in the FZG micropitting test.